Electrolytic removal of resin from metal



Patented Sept. 6, 1949 NITED ST TES ieTENT oFFICE ELECTROLYTIC REMOVAL OF RESIN. FROM METAL Max Frager and Hyman Iserson,

Philadelphia, Pa.

N Drawing. Application March 14', 9 .7 Serial No. 734,8 4

e ol ims. (o1. ge -14,1)

(Granted 4 under a mended Ap il The invention described and claimed herein may be practiced and used by .or for the United -States Government for governmental purposes, vwithout payment? to us of any royalty therefor.

This invention relates to the removal of films or thin coatings of resin from metallic articles to which they have been applied.

' and hardened on the metal for a long time andat elevated temperatures) by treating the cartridge case or other workpiece in an electrolytic bath in which the workpiece forms the positive pole or anode. I

Pri r o th s nven i n sandb n wa the most positive method known for removing such films. Sand-blasting isobiectiona e, w because of the resulting surface roughness which occurs and because only a few industrial establishments are equippedto sand -blast work on a I production basis at areasonable cost.

The most satisfactory chemical methods .to date have required the use of hot caustic solutions sometimes containing cresylic acid. This type of procedure, however, is not effective with all the phenolic varnish films which are encountered in practice. Other chemical methods have been used by which the use of combinations of caustic solutions and acid treatments has had better success in some cases.

One example of our invention which has been found to be operative in practice is the following:

A steel cartridge case three inches in diameter and bearing a cured coating of unmodified phenol-formaldehyde resin to a thickness of from three to six ten thousandths of an inch is immersed in an electrolytic bath comprising a solution of sodium hydroxide (NaOH flake caustic) parts by weight) and tap water (85 parts by weight). The cartridge case is connected as the positive pole or anode to a source of direct current electricity. As an optimum, a direct current is passed at a current density of from 13 to 27 amperes per square foot. The optimum temperature of the bath is from 200 to 220 degrees Fahrenheit. Treatment for fifteen minutes results in complete removal of the film. Thicker films require a longer treatment. Upon removal of the film, the cartridge case is taken out of the bath. The bath fiuid adhering to it is then removed by water rinsing and air drying.

ct of March a, 1883 as me; an r "Th meme me 9? crea on 9? th pmcess o th s in ent n arrea s to b The caus ic attacks er w ake s e ei fi. so e xt t Th new lm m y a e e ceed eslrmi r hqles h u it The elect curren passes hr l heahle Be i 1 smooth, clean 1 ly metal.- thi au es an e i n of a ,Thegas .inturn peelsor strips the residue ofthe esin filmfreni th f actal" sl i aee e n a a1 surface which, if it has an 1 4. it he a e t 'Q med treatment) I iseasilycleaned by ordinary chemica cleanin me ods; such as P c in Obvigusly su h a euriaeei memeh e i e fu p a i s. .of. ei treatm nt seful en n som mea e The Beam coating is of corrosion hand in or m l ins der-lee emcee ayup .invd ed beiet the. wo is i en edd t me! t a ment- It wi l re eee r eo mzee t a h x s a more or less wide range of eduivalents for each 55 t ee ement o .ste 'g the s o hi i vention.

For example, the workpiece pr core (which is t be lean and, n wh c e re in fi or oa me is ate m e n m t llic -flee althei e ens nveht eniis Pa ti u a y u ble to ferrous metals and alloys.

Similarly, the coating to be removed may be a synthetic plastic capable of forming a thin film as, for example, unmodified, heat reactive, phenol formaldehyde varnish, or a baked varnish film such as those composed of cured thermosetting plastics.

This invention is also useful to remove vinyl resins and alkyd resins.

The bath preferably should consist of an alkaline electrolyte, especially one in a higher range of alkalinity. An example of a suitable bath is one containing sodium. orthosilicate with or without the addition of a detergent. Although ionizable sodium compounds have been preferred by us, it is obvious that other ionizable compounds, e. g., potassium compounds, would be quite satisfactory. In the use of the potassium basic compounds would prove slightly more effective than that of the sodium because of the higher ionic mobility of the former.

The temperature can be as low as that of the ambient atmosphere or as high as is dictated by the economic limits of heat and pressure which would be required.

Although making the workpiece anodic has been found to be more effective than cathodic electrolysis, the latter is, probably because of the N'AWM higher volume of gas evolution, of considerable value in removing the resin films. In the case of cathodic treatment, the film is sumciently loosened so that it can be readily removed by a strong stream or spray of water or steam or by additional mechanical treatment such as wiping or brushing.

The invention claimed herein is:

1. A method for removing from a, metal surface cured thermosetting synthetic plastics in a substantially pure form consisting of unmodified heat reactive resins, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of an alkaline metal hydroxide from the group consisting of sodium and potassium hydroxide and 85 parts by weight of water, and passing a, direct current of from 13 to 27 amperes per square foot through said bath and through said workpiece at a temperature of from 200 to 22 degrees Fahrenheit.

2. A method for removing from a metal surface cured thermosetting synthetic plastics in a substantially pure form consisting of unmodified heat reactive resins, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of sodium hydroxide and 85 parts by weight of water, and

passing a direct current of from 13 to 27 amperes 7 per square foot through said bath and through said workpiece at a temperature of from 200 to 220 degrees Fahrenheit.

3. A method for removing from a metal surface cured thermosetting synthetic plastics in a SlJ-b'.

stantially pure form consisting of unmodified heat reactive resins, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of potassium hydroxide and 85 parts by weight of water, and passing a direct current of from 13 to 27 amperes per square foot through said bath and through said workpiece at a temperature of from 200 to 220 degrees Fahrenheit.

4. A method for removing from a metal surface cured unmodified heat-reactive phenol formaldehyde coatings, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of an alkaline metal hydroxide from the group consisting of sodium and potassium hydroxide and parts by weight of water, and passing a direct current of from 13 to 27 amperes per square foot through said bath and through said workpiece at a temperature of from 200 to 220 degrees Fahrenheit.

5. A method for removing from a metal surface cured unmodified heat-reactive phenol formaldehyde coatings, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of sodium hydroxide and 85 parts by weight of water, and passing a direct current of from 13 to 27 amperes per square foot through said bath and through said workpiece at a temperature of from 200 to 220 degrees Fahrenheit.

6. A method for removing from a metal surface cured unmodified heat-reactive phenol formaldehyde coatings, which method consists of immersing the workpiece in an electrolytic bath consisting of 15 parts by weight of potassium hydroxide and 85 parts by weight of water, and passing a direct current of from 13 to 27 amperes per square foot through said bath and through said workpiece at a temperature of from 200 to 220 degrees Fahrenheit.

MAX FRAGER. HYMAN ISERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 827,802 Hollis Aug. 7, 1906 1,457,688 Bohnhardt June 5, 1923 OTHER REFERENCES The Cleaning of Metal, by Mitchell (Magnus Chemical 00.), 1930, page 56.

Metal Industry, July 7, 1944, page 8.

"Modern Plastics Catalogue, Oct. 1938, table following page 172; Dec. 1941, pages 59, 60, 61. 

